The present invention relates to data transfer from a disk drive. More particularly, the present invention relates to a sequential data transfer control and correction mechanism in a disk drive for use in transferring large files at a constant data rate.
In Audio/Video (AV) applications, it is essential that a source of the audio or video data (e.g., a local disk drive, network server, etc.) maintain a constant data rate to the host to ensure acceptable picture and sound quality. The host may be, for example, a personal computer. Typically, when the source is a local disk drive within the personal computer, there are settings in the drive to ignore errors during a transfer in order to maintain the minimum flow of streaming data. Data read errors are handled by re-reading the data by a mechanism called a xe2x80x9cretry.xe2x80x9d Each retry to re-read data takes at least one disk revolution. If the disk drive is set to ignore errors, faulty data may be sent to the host. Because the faulty data is part of a video or audio stream, the viewer is typically subjected to a very short burst of xe2x80x9cnoisexe2x80x9d and/or loss of picture until good data is again received by the host. Such noise is distracting and detracts from the viewer""s enjoyment of the audio and video program.
With the advances in disk drive technology, including faster transfer rates and greater capacity, more and more audio and video data is being stored on disk drives. Accordingly, there is a need for a disk drive that will maintain a constant data rate, while minimizing the amount of faulty data that is transferred to the host. The present invention provides such a solution.
The present invention is directed to a sequential data transfer control mechanism for use in a media drive, such that a minimum or constant data rate to a host is sustained while providing a method for allowing retries and accesses to reallocated sectors if the disk drive""s recent historical performance has been sufficient to guarantee that the minimum or constant data rate will be met while performing a retry or accessing a reallocated sector. During the transfer of data, the disk drive determines a reserve value that represents the amount of data that is stored in a transfer buffer. The reserve value is increased by the number of sector of data actually sent to an intermediate buffer between the disk drive and the host, and decreased based on the minimum or constant data rate, normalized to revolutions of a disk within the drive. Based on this value, it is determined if the disk drive can seek for data in reallocated sectors or perform retries to correct faulty data when errors occur. Because disk drive electronics provide automation for the transfer portion, the process of performing retries and seeks may be programed into the disk drive hardware such that specific conditions may be set under which the disk drive may stop transferring data and perform a retry or seek to a reallocated sector location. When particular error conditions are encountered, and the reserve value exceeds the minimum or constant data rate, there is enough data in the buffer to perform a retry. Also, when other error conditions are encountered and the reserve value exceeds a higher threshold (e.g., approximately 4 times the constant data rate), there is enough data in the buffer for the disk drive to seek to a reallocated sector""s location on the disk, read it, and return to continue the transfer of data to the host.
Other features and aspects will be described herein.